[Sujective evaluation of the duration of sleep periods: role of actual time and the representation rate of different EEG stages].

Subjective estimations of the duration of night sleep periods and their actual duration were compared in 29 healthy men 21--36 years of age, awoken from the night sleep. The comparisons concerned the duration of consecutive sleep cycles, long (almost whole sleep cycles) and short ("parts of the cycles") periods, short periods ("parts of the cycle") without REM and with it. It has been found that long and short sleep periods are correspondingly reflected in the subjective estimation of their duration. The comparison of the estimation rates of various stages revealed that the highest subjective estimation, reduced to an hour of real time (subjective "hour estimation") in the first three sleep cycles characterises the cycle parts, including REM, whereas the lowest one--cycle parts, represented only by slow sleep stages, including delta-sleep. Subjective estimation of the sleep cycle duration regularly lowers throughout night sleep from evening till morning. Thus, subjective estimation of the duration of sleep periods is determined by two factors: their actual duration and manifestation rate of different sleep stages. The course of subjective time count in the sleep cycle seems to be uneven: it is slowed down in delta-sleep and accelerated in REM sleep following delta-sleep.